Up to now, a general needle valve includes a valve casing having a hollow box structure and including a flow inlet port and a flow outlet port, and a valve rod screwed into a lid of the valve casing so as to be retractable. By vertically moving the valve rod while rotating, an opening degree of a flow path inside the valve casing is adjusted. In this structure, the valve rod moves in a longitudinal direction thereof while rotating, so a sealed portion between the valve rod and the valve casing is less durable, and there is a fear in that fluid may leak from the sealed portion.
In view of the above, JP2003-329698A (paragraphs [0044] to [0052] and FIG. 1) proposes a structure in which a male screw (13f) of a valve rod (13e) is retractably screwed into a female screw (14a) fixed to a valve casing (11), a valve body (15) is additionally provided to a lower end portion of the valve rod (13e), and the valve body (15) is vertically moved with respect to a needle guide (11e). According to the invention described in JP2003-329698A, owing to a mechanical function of a stopper mechanism (16), a stepping motor is driven until a rotor (13) is forcibly stopped, to thereby obtain an origin.